Box Sync 4.0 provides detailed user notifications if there an issue syncing a file or folder.
Box syncs files based on the file size eligibility of the file owner. The maximum file size limit for uploads to Box varies depending on the file owner’s account type. For file size limits, see What's the maximum file size I can upload?
If you are unable to sync a file in Box because of the inherited file size limits, be sure to alert the file owner.
All devices with Box Sync installed.
Check with the file owner, and ensure that the file being synced is under the owner's maximum file size limit.